Progressive multifocal leukoencephalopathy (PML):
A demyelinating disease which results from the reactivation of John Cunningham virus (JC virus) infecting oligodendrocytes in patients with compromised immune systems.
🧠CT: Asymmetric low attenuation in periventricular and subcortical white matter, contrasting with symmetrical hypoattenuation in HIV encephalopathy.
MRI:
🧠Multifocal, asymmetric periventricular and subcortical involvement with minimal mass effect/enhancement.
🧠U-Fiber Involvement: Common in parieto-occipital regions; sharp peripheral border, hazy inner border.
🧠Signal Characteristics: T1: Hypo intense, T2: Hyperintense, no enhancement, patchy DWI restriction at lesion edges.
🧠Signs:
💫Milky Way Sign: Punctate high T2 signal lesions.
🏋️♀️Barbell Sign: Abnormality crossing the splenium.
🦐Shrimp Sign: Sparing of the dentate nucleus in the cerebellum.
🧠MR Spectroscopy: Reduced NAA, increased choline/lipids, lactate presence.
🧠MR Perfusion: Elevated at lesion edges, notably in progressive non-IRIS PML.
Source: Radiopedia
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